Manually operated machines have been used for many years in hardware stores, fabricating operations, etc., for cutting sheets of various materials into pieces. Such machines have conveniently taken the form of vertically mounted wall units comprised of a horizontal shelf for supporting the sheet stock, and parallel vertical tubes for guiding the cutting head. Interchangeable cutting elements are generally provided, including a wheel for driving a fissure in glass, and blades for scoring plastic and for slicing cardboard, foam core mat, and like materials.
The glass and plastic sheets must be separated, or "broken out", following scribing or scoring, since the cutting element does not normally completely sever the material. For this purpose an inverted V-shaped anvil may be positioned along the cutting path, to provide an underlying raised ridge upon which the scored sheet may be forced and broken.
In the case of glass, which has a very high modulus of elasticity, the simple hand application of a bending moment at the bottom of the score is generally sufficient to instantaneously complete the cut. Plastic, however, is much more difficult to sever because of its relatively low modulus of elasticity.
Thus, as the bending moment is applied and the cut begins to propagate, or run along the sheet, the point of severance becomes progressively further from the point at which the force is applied. This, and the inherent flexibility of the plastic material, make it extremely difficult to maintain a breaking moment at right angles to the score line; the break-out therefore tends to veer away from the score and to wander, following a random but generally curved path.
Prior art machines have endeavored to overcome this difficulty by use of a separate break-out tool, in the form of a hand lever, as described in Insolio et al U.S. Pat. No. 3,889,862. In use, the tool is inserted between the parallel guide tubes of the machine and the plastic sheet, and is forced upon the sheet to run the score a distance of several inches; the lever is moved progressively along the score line to produce a series of snapping actions, ultimately to separate the pieces along the entire length of the sheet. Although effective, the quality of the cut edge produced in this manner tends to be inconsistent, revealing minor aberrations where each short break terminates.
Other U.S. patents which disclose means for cutting glass and/or plastic include the following: U.S. Pat. Nos. 2,814,163 Krulwich; Oakley 3,138,308; LeGras 3,259,286; Insolio et al 3,399,586; Augustin et al 3,532,260; Stehle et al 3,587,953; Wakabayashi et al 3,866,449; Insolio 4,005,808; Insolio et al 4,009,813; and Insolio 4,018,372. Krulwich, for example, describes the use of a spring plate as a mandrel for breaking scored glass sheet, and LeGras uses a "diablo" to apply bending force for the same purpose. No. 4,005,808 to Insolio is directed to a cutting method for plastic, in which a scoring tool is inserted into a cross-slide to produce a score-line in the plastic sheet. The tool is thereafter inverted and used to force a V-shaped block toward a fixed mandrel, which deforms the sheet and creates a fissure; the sheet is then manually deflected to finally break the score. Insolio U.S. Pat. No. 4,018,372 teaches the use of spaced, prestress wheels in cooperation with an underlying reaction roller to cut relatively thick glass sheet. The cutting tool and the force-applying rollers are hydraulically operated for retraction and extension during appropriate phases of the operation.
A highly effective manual cutting machine is commercially available from the Fletcher-Terry Company of Farmington, Conn., which is designed for use with interchangeable pillar posts having cutting elements for plastic, glass and mat. The pillar post assembly is supported by a floating rocker arm, which is spring loaded to maintain a uniform force during the cutting or scoring operation, and a trigger arm is provided to elevate the cutting tool at the completion of the cutting stroke. The cutting head is slidably supported upon parallel tubular guide rails by bearing mounts which extend laterally from its opposite sides.
Despite all of such activity in the art, still a demand remains for a manual sheet cutting machine that is capable of smooth and highly effective operation to produce optimal scoring of glass and plastic sheets, and to produce high quality cutting of any of a variety of materials.
Thus, primary objects of the present invention are to provide a novel cutting head, and a novel manual sheet cutting machine utilizing such a head, which are highly effective and facile to use for cutting glass, plastic and mat materials, and by which cuts of high quality can readily and consistently be produced.
Another object of the invention is to provide such a cutting head and machine which are of relatively uncomplicated design and durable construction, and are smooth and comfortable in operation.